Package googleapiclient :: Package discovery_cache :: Module file_cache
[hide private]
[frames] | no frames]

Source Code for Module googleapiclient.discovery_cache.file_cache

  1  # Copyright 2014 Google Inc. All Rights Reserved. 
  2  # 
  3  # Licensed under the Apache License, Version 2.0 (the "License"); 
  4  # you may not use this file except in compliance with the License. 
  5  # You may obtain a copy of the License at 
  6  # 
  7  #      http://www.apache.org/licenses/LICENSE-2.0 
  8  # 
  9  # Unless required by applicable law or agreed to in writing, software 
 10  # distributed under the License is distributed on an "AS IS" BASIS, 
 11  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
 12  # See the License for the specific language governing permissions and 
 13  # limitations under the License. 
 14   
 15  """File based cache for the discovery document. 
 16   
 17  The cache is stored in a single file so that multiple processes can 
 18  share the same cache. It locks the file whenever accesing to the 
 19  file. When the cache content is corrupted, it will be initialized with 
 20  an empty cache. 
 21  """ 
 22   
 23  from __future__ import division 
 24   
 25  import datetime 
 26  import json 
 27  import logging 
 28  import os 
 29  import tempfile 
 30  import threading 
 31   
 32  from oauth2client.contrib.locked_file import LockedFile 
 33   
 34  from . import base 
 35  from ..discovery_cache import DISCOVERY_DOC_MAX_AGE 
 36   
 37  logger = logging.getLogger(__name__) 
 38   
 39  FILENAME = 'google-api-python-client-discovery-doc.cache' 
 40  EPOCH = datetime.datetime.utcfromtimestamp(0) 
 41   
 42   
43 -def _to_timestamp(date):
44 try: 45 return (date - EPOCH).total_seconds() 46 except AttributeError: 47 # The following is the equivalent of total_seconds() in Python2.6. 48 # See also: https://docs.python.org/2/library/datetime.html 49 delta = date - EPOCH 50 return ((delta.microseconds + (delta.seconds + delta.days * 24 * 3600) 51 * 10**6) / 10**6)
52 53
54 -def _read_or_initialize_cache(f):
55 f.file_handle().seek(0) 56 try: 57 cache = json.load(f.file_handle()) 58 except Exception: 59 # This means it opens the file for the first time, or the cache is 60 # corrupted, so initializing the file with an empty dict. 61 cache = {} 62 f.file_handle().truncate(0) 63 f.file_handle().seek(0) 64 json.dump(cache, f.file_handle()) 65 return cache
66 67
68 -class Cache(base.Cache):
69 """A file based cache for the discovery documents.""" 70
71 - def __init__(self, max_age):
72 """Constructor. 73 74 Args: 75 max_age: Cache expiration in seconds. 76 """ 77 self._max_age = max_age 78 self._file = os.path.join(tempfile.gettempdir(), FILENAME) 79 f = LockedFile(self._file, 'a+', 'r') 80 try: 81 f.open_and_lock() 82 if f.is_locked(): 83 _read_or_initialize_cache(f) 84 # If we can not obtain the lock, other process or thread must 85 # have initialized the file. 86 except Exception as e: 87 logging.warning(e, exc_info=True) 88 finally: 89 f.unlock_and_close()
90
91 - def get(self, url):
92 f = LockedFile(self._file, 'r+', 'r') 93 try: 94 f.open_and_lock() 95 if f.is_locked(): 96 cache = _read_or_initialize_cache(f) 97 if url in cache: 98 content, t = cache.get(url, (None, 0)) 99 if _to_timestamp(datetime.datetime.now()) < t + self._max_age: 100 return content 101 return None 102 else: 103 logger.debug('Could not obtain a lock for the cache file.') 104 return None 105 except Exception as e: 106 logger.warning(e, exc_info=True) 107 finally: 108 f.unlock_and_close()
109
110 - def set(self, url, content):
111 f = LockedFile(self._file, 'r+', 'r') 112 try: 113 f.open_and_lock() 114 if f.is_locked(): 115 cache = _read_or_initialize_cache(f) 116 cache[url] = (content, _to_timestamp(datetime.datetime.now())) 117 # Remove stale cache. 118 for k, (_, timestamp) in list(cache.items()): 119 if _to_timestamp(datetime.datetime.now()) >= timestamp + self._max_age: 120 del cache[k] 121 f.file_handle().truncate(0) 122 f.file_handle().seek(0) 123 json.dump(cache, f.file_handle()) 124 else: 125 logger.debug('Could not obtain a lock for the cache file.') 126 except Exception as e: 127 logger.warning(e, exc_info=True) 128 finally: 129 f.unlock_and_close()
130 131 132 cache = Cache(max_age=DISCOVERY_DOC_MAX_AGE) 133